The problems plaguing WorldCom Inc.'s UUNet Internet backbone have been resolved, according to WorldCom, which cited route table problems as the source of Thursday's global Internet slowdown.

In a 5:19 p.m. ET statement, WorldCom said its UUNet service had been restored after a day of outages that WorldCom said affected 20 percent of its U.S. customer base. Because UUNet is a backbone that carries a significant portion of all Internet transmissions, its breakdown affected other ISPs (Internet service providers) and noticeably slowed Internet traffic worldwide.

Route tables are used to tell routers what to do with the traffic flowing over the Internet. Thursday morning, UUNet's route table loaded incorrectly, according to WorldCom. The company is still investigating the cause of the error, spokeswoman Jennifer Baker said.